When I worked for a used gear store (like a pawnshop that dealt with music gear only), our goal was 30% profit, we paid well so we got a lot of people bringing their stuff in. Granted, this was ~2003 when ebay was booming and stuff was easy to sell, we started all of our auctions at $1 for 3 - 5 days and pretty much knew what they would sell for. Now days that doesn't work, everyone knows to wait for the last seconds of an auction.